This program project focuses on immunologic events that trigger, sustain, or dampen immune responses in tissues, including: 1) the skin in graft versus host disease (GVHD);2) the gastrointestinal tract in inflammatory bowel disease (IBD) and GVHD;and 3) the heart, in cardiac allografts with chronic rejection. This core will be directed by A.J. Demetris, M.D;who has extensive experience in these areas and will be responsible for assuring that the principal roles of the core are fulfilled. The principal roles are to: A) Grade and stage each of the inflammatory diseases, described above, which are important endpoints for each of the three projects. B) Use detailed tissue sample analysis to help understand immunologic mechanisms contributing to, or preventing, the inflammation, tissue damage, and structural alterations. The core is designed and ideally situated to accomplish these goals as we have successfully fulfilled similar functions for more than 15 years at the Thomas E. Starzl Transplantation Institute. The laboratory utilized for the Histopathology Core is already fully functional and equipped to conduct routine and specialized tissue triage and analysis techniques, including grading and staging of inflammatory disease processes, characterization of cell phenotypes (and subtypes), and their interactions within systems. Furthermore, our considerable experience in computerized image processing and morphometry will enable quantitative analysis of observed phenomena to corroborate earlier, possibly quite subtle, qualitative changes. In addition, we have the capability to communicate results/data to off-site investigators using pre-existing whole slide digital imaging capabilities and telepathology software already in use for other projects in our laboratories.